The following discussion of the background art is intended to facilitate an understanding of the present invention only. The discussion is not an acknowledgement or admission that any of the material referred to is or was part of the common general knowledge as at the priority date of the application.
A surfboard, stand-up paddleboard (SUP), or similar type of board for use in water sports and other activities can be viewed in one sense as a summation of hydrodynamic surfaces. The surface of the bottom of the board in contact with water generates lift and affects speed. More importantly though, it is the fins working in collaboration with rail and bottom contour that most influence the feel of the board when changing direction. Since the form shape of surfboards including the rails and bottom surface has undergone finer and finer adjustments over the past few decades, the largest gains that can still be made to a board's performance is in fin modification.
Predominant factors that influence the effect of the fins include (i) foil shape, and the curve from leading to trailing edge as it changes from base to tip; (ii) template shape, which is the combination of depth, width, and rake that make up the profile of the fin; (iii) stability and flex, which can depend on the materials from which a fin is made; and (iv) fin placement, which comprises tow and camber of the fins, the distance between the fins, and the distance of the fins from the rear of the board.
Foils comprise surfaces which affect lift and drag. Where one surface of a foil is curved and the other, predominantly flat (a ‘flat foil’), it takes less effort (drag) for liquid to flow past the flat surface as the path of least resistance than the curved surface. As a result, more water will flow past the flat surface of the foil creating an area of high pressure. Conversely, an area of low pressure is created adjacent to the curved surface of the foil. This difference in pressure creates lift towards the curved side of the foil. The more curve a foil has, the more drag it induces over the curved surface which means that a foil with greater curvature will have more lift at lower speeds. The problem is at higher speeds that additional drag will develop turbulence and stall the flow across the foil. Side fins on a surfboard are usually flat foils which are oriented with the flat face of the foil facing towards the centre or stringer of the board. The resulting pressure differential assists to pull the board fins and rail of the surfboard down into the water. Therefore, thicker, more curved foils are preferred by surfers for slow waves, and flatter, finer foils for faster waves.
Template shape affects stability and control. As an example, fins that are deeper, with a wider base and more rake provide greater stability and control as a result of a relatively large surface area. However, more surface area causes greater drag and slows a board down. As a generalisation known amongst surfers, fins with a greater surface area are more preferred for steep and heavy waves, choppy and irregular conditions, for heavier surfers, and/or surfers with a flowing style. Alternatively, fins with less surface area are more preferred for sloped, clean and glassy waves, for lighter surfers, and/or surfers that exercise extreme and radical manoeuvres.
The flex of a surfboard fin can affect stability in turns. For example, a flexible tip on a fin can dampen or smooth out some of the bite when a surfer changes direction on a surf board. But a stable fin base is crucial to prevent or minimise turbulence which can generate drag and disturb the lift causing loss of fin control, making the board slow and out of control. Less flex can make turns more off a pivot.
‘Toe’ can be considered in terms of the angle the base of the side fins are pointed in towards the centre of the board relative to the leading edge and trailing edge at the base. ‘Cant’ can be considered in terms of the angle the body of a fin is set at relative to the bottom surface of the board in a plane perpendicular to the direction of the stringer. Both toe and cant affect the ‘angle of attack’ of fin foils in their movement through the water. A greater angle forces more water flow around the outside curved surface of the foil at lower speeds making it easier to initiate turns on slower waves. However, too much angle at higher speeds increases turbulence and drag slowing down the board.
Since the introduction of removable fins about two decades ago by FCS®, there has been a greater interest from surfers and particularly professional surfers in fin placement in addition to the other factors described above. While fin placement is often left to convention, for example, with many board shapers following the benchmark for approximate location set by Simon Anderson more than thirty years ago, many other board shapers have their personal preference for each surf board model they shape. There are, however, subtle differences in most boards and in all riders. An adjustment of the position of a fin as small as a 4 mm fin movement fore or aft in either or both the centre fin or side fins can have a profound effect on the performance of a board, similar to a change of fin size or template. In general terms, moving a fin towards the rear of the board will stiffen the board, allowing it to handle greater speed and irregular water conditions. Moving a fin forward will loosen the board allowing it to turn on a tighter radius for easier changes in direction, and is preferable in glassy water conditions and short beach surf breaks.
Removable fin arrangements and systems have therefore been designed, with some available for purchase, which allow a surfer to adjust the position of a fin on their surfboard, and in some cases, even the tow and cant of the fin. However, these removable and adjustable fin arrangements commonly attach to their own unique and custom fin box or plug requiring a new board or modifications to an existing board. Many of these adjustable fin arrangements also require tools to be carried by the surfer to adjust the position of the fins on the board. As a result, there has been a relatively small uptake of these adjustable fin arrangements by the millions of surfers and other board riders around the world.